The present invention relates to a process for the preparation of dienes and/or trienes by treating polymers with certain olefins in the presence of a disproportionation catalyst. The present invention relates in particular to a process for the preparation of dienes and/or trienes by treating polymers based on conjugated dienes having four or five carbon atoms with certain olefins in the presence of a disproportionation catalyst. Particularly, the present invention relates to a process for the preparation of at least one of isononadiene (2,6-dimethyl-1,5-heptadiene) and 2,6,10-trimethyl-1,5,9-undecatriene by treating polyisoprene with isobutene in the presence of a disproportionation catalyst.
It is known from British Pat. No. 1,264,127 that certain polymers can be broken down into smaller polyolefins by reacting them with a non-conjugated non-alpha olefinically unsaturated non-cyclic hydrocarbon in the presence of a complex homogeneous disproportionation catalyst. Alpha (or terminal) olefins have been suggested as suitable treating agents in, inter alia, U.S. Pat. Nos. 3,912,703 and 3,558,589, the latter disclosing preference for the use of internal olefins over terminal olefins.
A specific class of terminal olefins comprises alpha-olefins having two hydrogen atoms at the terminal carbon atom and no hydrogen atoms attached to the other carbon atom forming the terminal double bond, such as isobutene or derivatives thereof. This class of olefins appears to be rather unsuitable and is explicitly excluded in the definition of the olefinic reactants in both U.S. Pat. No. 3,912,703 (not complying with the definition of "non-tertiary acyclic olefin", column 4, lines 49-54) and British Pat. No. 1,264,127 (not complying with the structure given on page 3, line 57). Moreover, it was found that isobutene did not give a disproportionation reaction in the presence of a homogeneous disproportionation catalyst as disclosed in the aforementioned British Pat. No. 1,264,127; not even in the presence of a suitable olefin like cis-butene-2. The main reaction products observed originated from oligomerization and polymerization reactions.
It has now surprisingly been found that alpha-olefins having two hydrogen atoms at the terminal carbon atom and no hydrogen atoms attached to the other carbon atom forming the terminal double bond can be used to prepare dienes and/or trienes from polymers in the presence of a heterogeneous disproportionation catalyst.